In commonly owned U.S. Pat. Nos. 3,943,056 and 4,052,303 a centrifugal filter is described which basically comprises a rotary basket or drum which is centered on an axis and which is normally rotated at high speed about this axis. The drum is provided with a filter medium and forms an output chamber radially outside the filter and an input chamber radially inside it.
Material to be filtered, normally a liquid/solids suspension, is fed into the drum as it rotates. The solids are trapped against the filter medium to form a filter cake, and the liquid phase passes through this cake and the medium to the output chamber. To increase efficiency it is known to form the output chamber in two compartments, one radially outside or underneath the filter medium and one axially offset therefrom but communicating therewith via an appropriate passage. The two compartments are maintained full of the liquids to a radial depth reaching radially inward to the filter cake so a liquid continuum is formed that extends radially inward at least to the filter cake. A dip or siphon tube controls the liquid depth--measured radially in this type of system--in the outer compartment to control the pressure across the cake and thereby regulate the system throughput.
The drum normally has an outer imperforate wall and, spaced radially inward therefrom, an inner perforated wall that extends perfectly cylindrically and that in turn supports a mesh, which may be a textile, a perforated metal plate, or a metallic screen of fine or coarse mesh size. The filter cake in turn lies on this mesh. Obviously clogging is a problem with this type of filter, in particular when it is operated continuously for long runs.
In other systems the filter element is constituted and/or supported by axially extending rods between which the liquid can flow, with the rods forming a cylindrical or slightly frustoconical support surface. Such an arrangement is less prone to clogging and is inexpensive to manufacture. It is particularly likely to clog at the regions of reduced filtrate flow, normally at the ends of the filter passages remote from the end the filtrate is drawn off.